WAITING TOO LONG DOESN'T GIVE YOU THE RIGHT TO TEAR INTO THE WAITRESS!!
Did he have a fair complaint about the wait, or did he lose it the second he started name-calling?
At a sports bar, a customer who says he waited too long unloads on the staff with insults while they stand there and take it. They end up handing him his money and telling him to leave.
Slow service is a legit complaint. I'll give him that. If you sat there forever and nobody came back, asking for a manager and walking out is fair. That's the grown-up version, and it's what my wife and I would do.
What isn't fair is aiming it at the person carrying the plates. Servers usually don't control the kitchen, and the name-calling here is ugly. As parents, we want our boys to learn that how you treat the person serving you says more about you than anything else in the room.
The staff handled it about as well as anyone could. No yelling back, money returned, door pointed. That's how you end it without making it worse, and honestly it's a skill a lot of adults don't have.
Complain to the manager. Leave the waitress out of it.